(1) Field of the Invention
The present invention relates to improvements in an apparatus for tensioning or longitudinally sliding a rail of a laid track consisting of two rails fastened to ties by fastening elements to reduce a gap between adjacent ends of longitudinally successive rail sections to be welded together to form the rail, the fastening elements of the longitudinally successive rail sections having been loosened, which comprises a closed, ring-shaped mechanical structural unit including two longitudinally spaced pairs of rail clamping jaw means and two transversely spaced hydraulic cylinder-piston devices for operating the rail clamping jaw means, each device connecting respective rail clamping jaw means of said pairs.
(2) Description of the Prior Art
Such a rail tensioning apparatus has been used in preparing for the welding of the adjacent ends of longitudinally successive rail sections to form a welded rail, particularly in the welding process with a mobile flash-butt welding machine, as disclosed in the Plasser & Theurer prospectus entitled K355 APT, of February 1986.
The flash-butt welding heads in these machines exert a sufficient tensioning force on the rail sections to enable short rail sections to be welded together or to weld together longer rail sections if they are supported on rollers to reduce frictional resistance to a minimum. In end welds, the rails are lifted out of their fastening elements, and changes in the rail length due to welding are compensated for by inserting corresponding lengths of rail section. However, a relatively large tensioning force is required to provide flash-butt welded joints between longer rail sections, particularly when they are not supported on anti-friction rollers, in cases where so-called thermite weld joints are cut out, resulting in large welding gaps which must be replaced by flash-butt welded joints, as well as for end welds at temperatures below the normal welding temperature and continuous welded track rails.
U.S. Pat. No. 3,349,216, dated Oct. 24, 1967, discloses an electrically operated flash-butt welding head useful in rail welding operations, which comprises two welding halves displaceable with respect to each other and designed to clamp the adjoining rail sections and pull them together. The rail clamps constitute welding elements and have a common rotary axis wherealong they are displaceable by means of hydraulically operated cylinders. The piston rods of the operating cylinders connect the clamps and are arranged symmetrically with respect to the weld and are coplanar therewith. The rotary axis is constituted by a hollow rod containing a control valve for uniformly delivering hydraulic fluid to the operating cylinders and the control valve is actuated by an electromagnetic drive mounted on the rod.
British patent No. 1,294,216, published Oct. 25, 1972, discloses a hydraulic tensioning device for continuous welded rail, which is constituted by a ring-shaped structural unit comprising two longitudinally spaced pairs of rail clamping heads interconnected by tie members extending above and below the rail for rotation about a vertical axis. Short bell-crank levers connect the clamping jaws respectively with hydraulic cylinders and tensioning members extending in the direction of the rail and parallel to a horizontal plane passing through the rail. A manually operated pump delivers hydraulic fluid to the cylinders and when they are operated, the clamping jaws clampingly engage the rail web and, upon additional hydraulic pressure being applied, the clamped ends of the two adjoining rail sections, whose fastening elements have previously been loosened, are pulled together to reduce the gap between the adjacent rail section ends and enable them to be welded together. This device is relatively heavy and may be disassembled. The device is mounted on the rail sections at each welding site, dismounted after use and transported to the next site where it is mounted again and operated by the manually operated hydraulic fluid pump. To enable the device to be readily transported from welding site to welding site, it has been made as small and light as feasible, thus limiting the dimensions of the central space within the ring-shaped unit. Even so, the unit may weigh as much as about 400 kg and is, therefore, difficult to handle, which considerably delays the operations.
A similar, but much lighter and even smaller, rail tensioning device has been disclosed in British patent No. 1,161,307, published Aug. 13, 1969. This device has such small dimensions that its tensioning force suffices only for longitudinally sliding or stretching very short and light rail sections.
Another rail tensioning apparatus of this general type has been disclosed in British patent No. 2,183,275, published June 3, 1987. The apparatus comprises two longitudinally spaced pairs of rail clamping jaws respectively operated by hydraulic cylinder-piston devices arranged at each side of the rail. Each pair of rail clamping jaws comprises two bell-crank lever clamping jaws arranged mirror-symmetrically with respect to a vertical plane passing through the rail and arranged in the same horizontal plane. Pivot axles link the lever clamping jaws to detachable holding members which interconnect the clamping jaws, the two longer lever arms of one of the clamping jaws of each pair being linked directly to the two operating cylinders and the two longer lever arms of the other clamping jaws of each pair being linked directly to the relatively long piston rods of the cylinders. The four shorter lever arms have arcuate clamping jaws for engaging the rail web. This apparatus, too, is manually transported from welding site to welding site and must, therefore, be relatively small and light. It is used to provide a mechanical connection between rail section ends by means of insulated fish plates. The width of the apparatus transversely to the rail is quite small, the spacing between the piston rods being the same, or only a little greater, than the mechanical connection itself.
European patent No. 132,227, published Jan. 23, 1985, discloses a ring-shaped rail tensioning unit for use in welding together the adjacent ends of rail sections. This unit is designed for longitudinally, vertically and laterally displacing a respective rail section end for centering the same with respect to an adjacent rail section end before the ends are welded together. It is a rather complicated device including a number of servomechanisms and provides a central space holding a shearing device with cutters for removing the weld seam. As the drawing clearly shows, this space is much too narrow to hold a flash-butt welding head.
The welding machine disclosed in U.S. Pat. No. 4,272,664, dated June 9, 1981, provides a hydraulic support shoe for the machine frame to relieve the track rails of the machine weight before the welding. The thus relieved rail may then be slid more readily to reduce the welding gap.